1. Field of the Inventions
The present invention relates generally to catheters.
2. Description of the Related Art
Catheters, which are in widespread medical use today, allow physicians to gain access into interior regions of the body in a minimally invasive manner. Catheters are frequently used to advance electrodes, biopsy devices, and other operative elements through bodily lumens to an intended treatment site. In cardiac treatment, for example, the catheter is steered through a main vein or artery into the region of the heart that is to be treated.
Although precise control of catheter movement is of paramount importance in all catheter-based procedures, the need for careful and precise control over the catheter is especially critical during certain procedures concerning the heart. These procedures, called electrophysiological therapy, are becoming more widespread for treating cardiac rhythm disturbances. Cardiac tissue coagulation (sometimes referred to as "ablation"), where therapeutic lesions are formed in cardiac tissue, is one procedure in which the ability to precisely position the distal end of the catheter is especially important. Incremental distal end movements of 1 mm to precisely position electrode(s) carried on or near the catheter tip are not uncommon and it can take up to an hour to precisely position the tip. In those instances where multiple electrode distal assemblies are employed, it is important that all of the electrodes achieve intimate tissue contact.
Some catheters are steerable in that the distal tip can be manipulated by way of, for example, a distal tip steering mechanism that is operably connected to the catheter handle by a steering control wire. Other catheters are not steerable. Steerable catheters typically include an elongate guide coil that extends from the proximal end of the catheter to a point proximal to the distal end. The steering mechanism consists primarily of a steering center support (also referred to as a "steering spring") that extends from the distal end of the guide coil to the distal tip of the catheter. The inventors herein have determined that the configuration of the steering mechanism in conventional steerable catheters, including the location at which the steering wires are attached to the center support, makes it difficult for conventional catheters to obtain intimate tissue contact.
Whether steerable or not, there are often instances where the physician will attempt to control the position of the distal end of the catheter by rotating the handle at the proximal end. The ability of the physician to precisely control the location of the distal end is directly related to the fidelity of the catheter's transmission of torsional forces exerted on the proximal end to the distal end. The greater the fidelity, the greater the likelihood that the physician will be able to accurately place the electrodes or other operative elements within the patient.
Torque transmission is primarily a function of catheter configuration. Many outer catheter bodies are formed from two tubular parts, or members. The proximal member is relatively long and is attached to a handle, while the distal member, which is relatively short, carries the electrodes or other operative elements. In addition, the proximal member is typically formed from material, such as braided Pebax.RTM., which has better torque transmission properties than the distal member, which is typically formed from a softer, more flexible material such as Pebax.RTM., that is better for steering. The proximal and distal members are adhesive bonded together end to end over a sleeve in what is referred to as a "butt bond" arrangement, which provides some torque transfer between the proximal and distal ends of the catheter. There is also an adhesive bond between the proximal member and steering center support, which is enclosed in a sleeve. This bond forms the primary vehicle for torque transmission from the proximal member to the tip.
The inventors herein have determined that there are a number of shortcomings associated with the conventional arrangement. One shortcoming has to do with the fact that an adhesive bond is formed between a round component, the butt bond sleeve, and the outer surface of the steering sleeve. If the bond is incomplete or if the torque is too strong, the adhesive may break or the steering sleeve may tear, thereby freeing the steering spring to rotate. Also the steering spring may at times freely rotate within the steering sleeve. As a result, there is often adequate torque transmission from the handle to the distal end of the proximal member, but inadequate torque transmission along the distal member, thereby preventing precise tip placement within the patient.
The inventors herein have also determined that the conventional assembly techniques are time consuming and labor intensive, which makes them expensive, and also result in products that may not be as reliable as desired.